Quality Assessment of a Mediterranean Sea Reanalysis M. Adani, G. Coppini, C.Fratianni, P.Oddo, M.Tonani, GNOO, INGV Sez Bologna N. Pinardi, M. Zavatarelli, Univ. of Bologna V. Lyubartsev, S. Dobricic, CMCC, Bologna

Ocean General Circulation Model: OPA code ( Tonani et al., 2008 ) 1/16 x 1/16 and 71 unevenly spaced levels Daily Mean output: Temperature Salinity Velocities Wind Stress Sea Surface Height Heat Flux Water Flux Shortwave Radiation Observations: T/S in situ profiles (MedAtlas, MFS) SLA along track (T/P,ERS1,ERS2, ENVISAT,J1) Observations:  OI-SST Assimilation schemes: OceanVar (Dobricic, S., and N., Pinardi, 2007) SOFA (De Mey, P., and M. Benkiran, 2002) Assimilation schemes: RELAXATION Experimental set-up Atmospheric and hydrological forcing: ➔ ECMWF operational analysis + ERA15 ➔ Monthly mean climatological NCEP precipitation ➔ Monthly mean climatological river runoff (GRDC)

Experimental set-up cont. Data Distribution Examples of spatial distribution of in situ and satellite observations in one day.

Experiment NameDescription SIMForced simulation: OV-RERe-analysis using OceanVar (3dvar): SO-RE Re-analysis using SOFA (ROOI): 85-90; 93-96;00-07 restart from OceanVar Experimental set-up cont. Multivariate part of the error background covariance matrix (B) is common to both assimilation scheme and the observational error matrix (R) is identical. Major difference between the two implementations is that OceanVar uses a barotropic model to estimates the corrections on SLA and SOFA uses formula of level of no-motion. In the latter case the SLA data can be assimilated only in area deeper then 1000 meters resulting in 12% less satellite observations assimilated for SO-RE.

Results 1.Mediterranean Volume Temperature 2.Gibraltar advective/diffusive part 3.Solar radiation 4.Relaxation term relaxation data assimilation

Results cont. RMSE BIAS TEMPERATURESALINITY

Results cont. SLA RMSE

Large scale low frequency ocean variability

Mean circulation at 15 m

The interpretation Mean circulation in the m

Ionian reversal Strengthening of the Levantine circulation Decadal variability

The mean vs Eddy Kinetic Energy (EKE) 0-bot: 0,03 m s m: 0,07 m s -1 EKE is 70-90%of TKE

Water mass formation rates: results Four major events: 1)1987 for WMDW 2) for LIW, CDW and EMDW 3) for WMDW and EMDW 4) WMDW, EMDW and LIW WMDW EMDW CDW LIW Sv Eastern Med Transient

Conclusions Two re-analysis and a simulation has been carried out for the Mediterranean Sea from 1985 to All available in situ and satellite information for the past 23 years have been used with two assimilation schemes, a Reduced Order Optimal Interpolation scheme, so-called SOFA, and a three-dimensional variational scheme, so-called OceanVar. OV-RE gives better results for abundant data such as SLA, improving by about 10% the RMSE with respect to SO-RE, but giving the same RMSE of SO-RE for sparse data sets, such as temperature and salinity profiles. Reanalysis is a useful dataset to study the low frequency variability of the ocean References: M. Adani, S. Dobricic, N. Pinardi, 2011: Quality Assessment of a 1985–2007 Mediterranean Sea Reanalysis. J. Atmos. Oceanic Technol., 28, 569–589. doi: /2010JTECHO798.1 N. Pinardi, M. Adani, G. Coppini, C. Fratianni, P. Oddo, M. Tonani, V. Lyubartsev, S. Dobricic, M. Zavatarelli.. The Mediterranean Sea large scale low frequency ocean variability from 1987 to 2007: a retrospective analysis., in preparation.